Coupling connection between step-motor and control shaft



e. LANGER 3,443,401 COUPLING CONNECTION BETWEEN STEP-MOTOR AND CONTROL SHAFT May 13, 1969 Filed May 5, 1967 United States Patent O US. C]. 64-27 Claims ABSTRACT OF THE DISCLOSURE A coupling connection between the rotor of a stepmotor, and a control shaft to prevent inaccurate step rotation of the control shaft. The coupling connection comprises complementary connections between the rotor and the control shaft, that function to prevent rotor oscillation or swinging that may occur at the termination of the rotational movement of the rotor associated with each step movement thereof from being transmitted to the control shaft. Therefore, any inaccuracies that may be produced by the rotor at the end of a step interval is not coupled to the control shaft, and the step movement of the control shaft is thus made more precise.

CROSS REFERENCE TO RELATED APPLICATION Applicant claims priority from German patent application No. S 103,674, filed May 6, 1966, in Germany.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to electrical step motors, and has particular utility in the precision mechanical field wherein a control shaft is rotated in step manner; for example, the control shaft may be used to drive typewriter carriages or other such machines that operate at a fast rate of speed. In particular, the invention has utility where precision movement of the control shaft is essential and Where inaccuracies between successive step positions must be minimized.

Description of the prior art The prior art teaches the utilization of electrical step motors, wherein control current pulses are applied to rotate the rotor a predetermined fraction of a revolution. The stator may have a plurality of windings, each associated with one or more poles, and the rotor may comprise one or more poles. The rotor is rotated by motor action to successive positions in step manner by selective energization of the stator windings by the control pulses. However, at the end of the rotational movement of the rotor associated with successive steps, there is a tendency for the rotor to oscillate or swing about its final position, because its movement is terminated abruptly. Such oscillations may be transmitted to the control shaft and thus cause inaccurate movement thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a sectional view of a rotor connected to the control shaft, through the coupling device taught by this invention;

FIGURE 2 is a sectional view taken along section lines AA of FIGURE 1, illustrating the relative interaction between complementary members of the coupling device that connects the control shaft to the rotor.

DETAILED DESCRIPTION OF THE INVENTION FIGURE 1 shows control shaft 1 that may be utilized to drive a wheel (not shown) associated with various 3,443,491 Patented May 13, 1969 apparatus, such as a typewriter, in step manner. That is, the control shaft 1, and hence, any shaft or wheel to which it may be coupled, is rotated in steps comprising equal fractions of revolution.

Control shaft 1 is coupled to coupling delay device 27 by coupling bushing 2, which is secured to control shaft by screws 3. Coupling delay device 27 comprises flanged plate 25 extending from sleeve 24. Control shaft 1 extends through coupling bushing 3 and into a portion of the bore defined by sleeve 24-. Sleeve 24 and plate 25 may comprise an integral unit, and its rotational motion is transmitted to control shaft '1 through coupling bushing 2.

Further, with reference to FIGURE 2, it is seen that leaf spring 4 is affixed to plate 25 and comprises two coacting spring members 4' and 4" that extend from diametrically opposite points on the periphery of plate 25.

Flanged sections 5 extend from the face of coupling bushing 8 and define slits 5 and '5" that receive spring members 4' and 4", respectively, of leaf spring 4. The slits are wide enough so that there is a fixed amount of play between members 4 and 4" of leaf spring 4 and associated flanged sections 5, as will be explained hereinafter. Flanged sections 5 may comprise an integral extension of coupling bushing 8. Rotor 6 is secured to coupling bushing 8 of coupling delay device 27 through conventional coupling means 28.

Bearing support 11, supports bushings 9 and 10, and control shaft 1 extends through bushings 9 and 10 as illustrated. Pressure disc 21, is mounted adjacent bearing bushing 9, and defines a recessed portion that receives a lubricating disc 12, which may comprise felt material for example. Perforated disc 13 comprises a plurality of equally spaced perforations, 13a, defined near the outer periphery therof at equal radial distances from its center. Disc 13 is affixed to shaft 1 and rotates therewith, by ring nut 16, that secures disc 13 to flanged section 111 of control shaft 1 through ring 15. Coil spring 14, is wound around control shaft 1 between sleeves 17 and 18, and thus indirectly exerts a force on pressure disc 21 that may be varied by shifting the position of bearing bushing 10 relative to control shaft 1, thereby varying the elongation and hence the spring force of coil spring 14. Screw 19 locks bearing bushing 10 in fixed relation with control shaft 1. Screw 29 locks pressure disc 21 in fixed position relative to control shaft 1.

Pressure disc 21 is prevented from twisting about an axis normal to the longitudinal axis of control shaft 1a by threaded peg 20 which fits into complementary bore in bearing support 11, thereby providing a counter force to any twisting forces that may be applied to pressure disc 21 by bearing 22 and its associated spring 23. Bearing 22 is ball shaped and is received by bore 26, defined by bearing housing 11. It is dimensioned so that a portion of it may be forced into position within perforations 13a of perforated disc 13, by a second coil spring 23, which is variably positioned in bore 26, between bearing 22 and threaded peg 30. The position of threaded peg 30, may be varied with respect to the threads of bore 26, thereby varying the force applied by coil spring 23 to bearing 22.

The above-described embodiment of the invention, functions in the following way. Rotor 6 of step motor 7, rotates in step manner, as determined by conventional motor control apparatus (not illustrated). The movement of rotor 6 is delayed by the coupling device 27 which is coupled to control shaft 1. The time delay between rotational movement of rotor 6, and coupling of said rotational movement to control shaft 1, is produced by the interaction between leaf spring 4, coupling bushing 2, and flanged sections 5 of coupling bushing 8.

It is seen with reference to FIGURE 2, that there is a predetermined amount of play between members 4' and 4" of leaf springs 4, and slits 5', and 5", respectively. The play may be defined in degrees since rotational movement is involved, and is selected to be slightly greater than the angle by which rotating rotor 6 will move control shaft 1 beyond the rest or terminal position, following termination of the predetermined rotational movement of rotor 6 at the end of each step. This guarantees that any oscillation or swinging movement of rotor 6 about the rest position is not transmitted to control shaft 1. Thus, during each step rotor 6 rotates control shaft 1 from one rest position to the next, through coupling device 27, the rest or terminal positions being determined by the spacing between perforations 13a of perforated disc 13. The rotational movement of rotor 6 is sufficient to counteract the force of spring 23, and the subsequent rotation of control shaft 1 thereby forces bearing 22 out of contact with the particular perforation 13a into which it had been positioned by spring 23 during the previous step. That is, during a particular step, perforated disc 13 is rotated with control shaft 1 and thus perfortaions 13a are removed or rotated from their position adjacent bore 26. The solid portion of perforated disc 13 between successive perforations 13a effectively decreases the size of the opening available to bearing 22 and forces it into bore 26. Then as the successive perforation 13a, is rotated so as to be adjacent bore 26, hearing 22 is forced into locking contact therewith by spring 23. Thus, the rotational movement or angle of rotation of contact shaft 1 associated with each step is determined by the spaced distance between perforations 13a, because rotor swing or oscillation that occurs at step termination is not transmitted to control shaft 1 because of coupling delay device 27.

The delaying action of leaf spring 4 occurs, because of the play between leaf spring 4 and flanged sections 5. That is, as rotor 6 rotates, it rotates coupling bushing 8 to which it is connected. However, plate 25 which is coupled to control shaft 1, does not immediately rotate as a result of rotating coupling bushing 8, because of the play between spring members 4' and 4" of leaf spring 4, and flanged sections 5 that extend from the face of coupling bushing 8. However, the continuing rotation of coupling bushing 8, will eventually cause flanged sections 5 into contact with spring members 4' and 4", and consequently rotational movement will be transmitted after the initial time delay determined by the play to rotate perforated disc 13. However, the continuing rotation of coupling bushing 8 and particularly the coupling of its rotation to plate 25 through leaf spring 4, will bend spring members 4' and 4" and cause energy to be stored in said leaf spring.

When bearing 22 is moved from contact position with one perforation 13a to the next successive perforation 13a during a particular step, step motor 7 abruptly terminates rotation of rotor 6. At this point, leaf spring 4, springs back into the position illustrated in FIGURE 2. Further, as discussed above, there is enough play between spring members 4 and 4, so that any oscillation or swing of rotor 6 about the rest or terminal position is not transmitted to control shaft 1 through plate 25.

The coupling delay device 27 illustrated in FIGURE 2 will rotate relative to the position illustrated, during successive step intervals. However, at step termination, leaf spring 4 will return to the relative positions illustrated in FIGURE 2, wherein there is a predetermined amount of play between it and flanged sections 5, so that rotor oscillations or swing are not transmitted to control shaft 1.

Further, it is seen that the axial rotation of perforated disc 13 is controlled or guided by pressure disc 21, because perforated disc 13 rotates in a path defined thereby. It is forced into said recess by spring 14, as heretofore explained. The rotational movement of perforated disc 13 is thus attenuated to some degree by pressure disc 21, although the attenuation may be minimized if pressure disc 21 comprises self-lubricating material. Further, lubricated disc 12 serves to lubricate bearing 22 and coacting perforations 13a. Thus, the invention provides a control shaft which functions to provide accurate successive step movements, that are isolated from errors that may be transmitted by the drive shaft.

SUMMARY OF THE INVENTION This invention is concerned with control devices that function in step manner. It discloses a coupling delay device that initially delays transmission of the rotatable motion of a rotor to a control shaft. It comprises a leaf spring coupled to the control shaft that is received by slits defined by the coupling delay device, which functions to absorb any rotor oscillation or swing that may be pro duced at termination of rotor movement associated with a particular step. Further, it discloses a perforated disc that is rotatable with the control shaft and defines a plurality of equally spaced perforations at equal radial distances from its center. Operatively associated locking and spring means are positioned adjacent the perforated disc, to set termination of successive steps in association with the perforations. Guide means control the rotation of the perforated disc, and lubricating means are provided therebetween to minimize attenuation of rotational movement.

What is claimed is:

1. A coupling arrangement between a drive shaft (6) driven by a step motor and a control shaft (1) having successive time spaced operating steps comprising:

a bushing (8) connected to the drive shaft (6) defining at least one slit (5', 5");

a leaf spring (4) having at least one spring member (4, 4") connected to said control shaft (1), said at least one slit (5, 5") receiving said at least one spring member (4', 4") therein, said at least one slit (5', 5") and spring member (4, 4") having a predetermined amount of play therebetween;

a perforated disc (13) defining a plurality of successive spaced perforations located at equal radii from its center rotatably connected to said control shaft (1);

detent means (22) Operatively associated with said disc;

spring means (23) to force said detent means into said successive perforations 13a) as the control shaft (1) rotates, to set the terminating position of successive steps of the control shaft.

2. A coupling connection as recited in claim 1 further comprising stationary guide means (21) to guide rotation of the perforated disc (13).

3. A coupling connection as recited in claim 2 further comprising lubricating means (12) positioned between said guide means (21) and said perforated disc (13).

4. A coupling connection as recited in claim 3 wherein said lubricating means comprises a lubricated felt disc (12).

5. A coupling connection as recited in claim 4 wherein said guide means comprises a disc defining a recess to receive said lubricated felt disc (12);

a spring (14) forcing said perforated disc (13) into operative position with respect to the lubricated felt disc (12) and the guide means (21).

References Cited UNITED STATES PATENTS 729,649 6/1903 Nyberg 64-27 X 2,248,428 7/1941 Kamenarovic 64-15 2,624,017 12/1952 Putnocky 310-49 X 2,731,006 1/1956 Hensel 64-27 X 3,031,866 5/1962 Johnson 64-27 3,271,599 9/1966 Kohlhagen 310-49 X FOREIGN PATENTS 330,589 12/1920 Germany.

HALL C. COE, Primary Examiner.

US. Cl. X.R. 74-1041 

